I have an '82 Maxim 650 that I bought new in 1982. I have not used it for the last five summers (work required me to be travelling all the time) and this summer got it going again. I had the carbs cleaned, installed new spark plugs, changed oil/filter/final gear oil and bike was working good for about 400KM.

After that, the bike would start fine with full choke but after about 1 minute would start missing/sputtering/backfiring for 5 minutes and then would run fine after it was warmed up with no choke. I put in a second set of new plugs and the problem went away and it was working good. Now after about 200KM with the second set of plugs, it is doing the same thing - starting fine, missing/sputtering/backfiring for a bit, and then working fine. I am thinking of buying another new set of plugs (I am using the NGK model specified in the owners manual) but do not want to be buying new spark plugs every 200KM. Anyone have any ideas as to what is happeing with my baby??

Sounds like you are flooding your cylinders and fouling the plugs. After cranking reduce the choke to where it is barely on. Another thing to do is pull the plugs when they are missing and see if they are sooty black. If so , then it is too much choke. Remember that the choke on these bike works not by reducing the amount of air to enrich the mixture but by adding more fuel.

Thanks for the advice. I will try reducing the choke after it starts and see if that helps. I will also pull the plugs and see if they are black right after it is backfiring. Drove the bike to work this morning and there was hardly any backfiring. (put a new air filter in it last night). Took a road where engine RPM were 3000-4000 rather than the highway and it seemed to work better. I will keep you posted!